1. Field of the Invention
The present invention relates to a centrifugal type blower unit which reduces noise generated therefrom without greatly reducing air-blowing capacity. The blower unit is suitable for a vehicle air conditioner.
2. Description of Related Art
In a conventional blower unit, noise (hereinafter referred to as "first noise") may be generated when air blown from a centrifugal fan collides with a nose portion of a scroll casing. The first noise is approximately proportional to a rotation speed of the centrifugal fan and number of blades of the centrifugal fan. Therefore, in the conventional blower unit, the shape of the nose portion is suitably formed so that the first noise can be decreased.
However, according to an experiment of the inventors of the present invention, noise (hereinafter referred to as "second noise") having a frequency approximately similar to the first noise is also generated in the conventional blower unit where a filter is disposed at an air suction port of the centrifugal fan. To reduce the second noise, the inventors of the present invention experimentally perform the method for reducing the first noise. However, the second noise cannot be sufficiently reduced by using the method for reducing the first noise.